Climate Change

Corals are extremely sensitive to temperature changes. This makes increased water temperatures a major threat for these creatures. Have you ever seen those corals that are so white they look like they have been bleached?

A Bleached Coral

Bleach Corals

Well, when the water temperature rises from 1.8 to 3.6 degrees Fahrenheit above the ceiling summer temperatures, the corals undergo a stress response, where the microscopic algae (zooxanthellae) is expelled. This is called coral bleaching, where all that remains to the visible eye is the white exoskeleton of the corals. Without the symbiotic algae, the corals will die unless they take up another zooxanthellae. Their survival also depends on the duration and level of temperature stress. Even if the corals do recover, they are likely to have reduced growth and reproduction, as well as be less resilient to diseases.

The year 1998 was when the strongest sea surface warming event ever recorded – the El Nino event. That year proved to be extremely devastating to reefs all over the word, where 16% of them were destroyed. Sad to say, the warming events and bleaching has persisted since then.

Rising Sea Level

Another challenge faced by coral reefs is the rising sea level due to global warming. Since 1870, there has been an increase of 20cm in sea level, and currently the rate of rise is at 3.4mm each year (and it’s accelerating).  This sea level rise will be likely to affect the amount of sunlight that can reach coral reefs. Coupled with slow reef growth, it could lead to “drowned reefs” where they are unable to build reefs to keep up with rising sea levels.

Scientists also predicted that with warming seas come tropical storms at a higher frequency. This does not fare well for the reefs as storms can reduce the reefs to mere rubble. Recovery then, will takes years or even decades. A study published in Science recently showed the bleak future of reefs: with the current rate of increase in global emissions of greenhouse gases, coral reefs face extreme reduction in habitat complexity and biodiversity.